We address these needs using a set of novel global climate model sensitivity experiments that explicitly incorporate SOC in soil hydraulic parameter calculations. Specifically, we use the coupled atmosphere-ocean NASA GISS ModelE2 to conduct three experiments with modern boundary conditions: 1) a “no landuse” scenario in which SOC reflects pre-agricultural conditions ~10,000BC (NoLU), 2) a scenario where SOC reflects 2010 landuse (crop+pasture) (SOC2010), and 3) a uniform 80% SOC reduction across agricultural regions, an approximate maximum amount estimated for the most severely degraded areas (SOC80) (Lal 2004; Sanderman et al. 2017). The NoLU and SOC2010 experiments utilize SOC and textural datasets created by state-of-the-art machine-learning techniques detailed in Sanderman et al. (2017) and Hengl et al. (2017), respectively. The SOC80 experiment serves as an “upper limit” to help us assess at what magnitudes do SOC changes induce significant hydroclimate impacts.
As an example of how these SOC scenarios impact our input soil hydraulic parameters, Figure 1 shows the changes (relative to NoLU) in saturated water content and hydraulic conductivity corresponding to SOC2010 and SOC80. Under SOC2010 conditions, major European and East Asian agricultural zones show between 5-10% declines in these parameters, which could lead to potential reductions in plant and crop water availability. Decreases in these parameters are amplified under SOC80 conditions, exceeding 10-15%+ across most areas.
We present our experimental results showing how these SOC changes impact critical soil moisture thresholds, surface energy fluxes and partitioning, and drought dynamics across major agricultural regions. We further explore how SOC changes affect regional resiliency to droughts of varying intensities and durations. This study motivates the needs to better understand the role of SOC in regional hydroclimate dynamics, particularly in relation to future landuse trajectories and climate change, and improve these representations in ESM frameworks.
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